How Do I Simplify the Function f(x) = cos(x)(3cos(3x)) + (sin(3x))(-sin(x))?

[Gill]

hey, i need to simplify this, and I am having a brain fart ...can u help me?

f(x)= cosx(3cos3x) + (sin3x)(-sinx)

i then have to find f(pi/6), but I am hoping i can do that once this is simplified...

thanks
Gill

 

[maverick6664]

hey, i need to simplify this, and I am having a brain fart ...can u help me?
f(x)= cosx(3cos3x) + (sin3x)(-sinx)
i then have to find f(pi/6), but I am hoping i can do that once this is simplified...
thanks
Gill

I wonder you made a typo... is cosx(3cos3x) $$\cos(x*3\cos(3x))$$ or $$\cos(x)*3\cos(3x)$$? Please place braces and it will clarify. But as for f(pi/6), it looks easy in any typo cases, because $$\cos(3*\pi/6) = 0, \sin(3*\pi/6) = 1$$